HARRISBURG, Pa. (AP) -- President Donald Trump on Thursday postponed a campaign rally scheduled for next week in the Pittsburgh area, the early political hotspot of 2018's congressional elections.

Trump's campaign said the decision was out of respect and sympathy for the victims and survivors of the Florida high school shooting that left 17 dead. It said another rally would be scheduled soon.

The rally would be Trump's second visit to Pennsylvania's 18th congressional district, where a new Monmouth University poll shows a close race. Trump, Ivanka Trump and Vice President Mike Pence have visited the district in recent weeks, ahead of March 13's special election in a contest widely seen as a test of whether Trump's party can stave off Democratic gains in the fall elections.

The Monmouth University poll, released Thursday, shows Republican Rick Saccone at 49 percent and Democrat Conor Lamb at 46 percent in a district won handily by former Republican Rep. Tim Murphy eight times over 16 years.

Trump trounced Democrat Hillary Clinton in the district in 2016 by almost 20 percentage points.

The special election is to pick a successor to Murphy, an abortion rights opponent who resigned in October after his hometown newspaper reported he suggested a mistress get an abortion when they thought she might be pregnant.

Millions of super PAC dollars are flowing into the race for the seat, practically all of it to support Saccone, 60, a four-term state representative and retired Air Force intelligence officer.

Lamb, a 33-year-old former federal prosecutor and ex-Marine, reported entering 2018 with more than twice the cash in his campaign account as Saccone, $412,000 to $200,000.

Outside groups have spent more than $5 million on the race, according to Federal Election Commission filings.

That includes about $2 million spent on TV ads by the Congressional Leadership Fund, a political action committee aligned with House Speaker Paul Ryan, and another $1 million spent almost entirely on TV ads by two groups - Ending Spending and 45 Committee - supported by Joe Ricketts, a Wyoming billionaire and TD Ameritrade founder. The National Republican Congressional Committee and the Republican National Committee have spent another $1.5 million combined.

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This story has been corrected to show that Rick Saccone is 60 years old, not 59.